Urothelial carcinoma of the bladder (or bladder cancer, BC) is one of the most common cancers in the Western world. Because high-grade invasive bladder cancers (HGIBC) can progress to life threatening metastases, identifying a natural compound that specifically inhibits BC invasion and metastasis is of tremendous importance for potentially reducing mortality as a result of this disease. Isorhapontigenin (ISO) i a new derivative of stilbene, and isolated from a Chinese herb that has been used in China for treatment of BCs for hundreds of years without understanding of molecular mechanisms. Thus, the goal of this proposal is to determine the ISO potential therapeutic effect and the molecular mechanisms responsible for this anti-cancer activity. Our preliminary studies found that the X-linked inhibitor of the apoptosis protein (XIAP) was extremely highly expressed in all of the human invasive BC tissues that were tested, but it was barely detectable in all adjacent normal bladder tissues, and that XIAP expression level was also markedly elevated in BBN-induced invasive BC tissues in p53-/-/pRb-/- mice as compared with that from wild-type mice and oncogenic Ras- induced low-grade BCs. We also found that XIAP was significantly higher in cultured human BC cells derived from HGIBC than from those derived from low-grade papillary bladder tumors (LGPBT). Moreover, we showed that treatment of BC cells with ISO inhibited HGIBC T24T cell migration and invasion, was accompanied with specific inhibition of Sp-1 transactivation and XIAP downregulation at the transcription level without affecting cell proliferation at doses of 5-10 ?M. Thus, we hypothesize that ISO is an effective therapeutic agent for the inhibition of BC invasion in vitro and BC invasion and metastasis in vivo via downregulation of the Sp-1/XIAP pathway. We will test this with the following aims: 1: To test the hypothesis that XIAP downregulation by ISO is responsible for its inhibition of BBN-induced BC formation in the mice lacking both p53 and pRb; 2: To evaluate the hypothesis that SP-1 is a major target for ISO downregulation of XIAP in BC in vitro and in vivo; 3: To define the molecular mechanisms whereby ISO inhibits the BC development in vitro and in vivo. Success of the proposal will facilitate our understanding of the molecular mechanism(s) responsible for the anti-cancer effects of ISO compound. This novel finding will provide valuable information for the design of more effective strategies for utilization of ISO or for the synthesis of other novel conformation- constrained derivatives for the treatment of BCs and other cancers. Taken together with the fact that BC is the most common malignant tumors, responsible for 336,000 new cases and 132,000 deaths annually worldwide, the studies should in turn help improve the clinical outcome of patients with BCs.